Description (Adapted from applicant's description): The goal of this project is to identify distinct subtypes of autism disorder and to map the loci biological or behavioral differences (neurobiological phenotypes) among patients diagnosed with AD. For stable differences they will study first-degree relatives to establish the trait is familial and to identify genetic patterns of transmission. Then they will apply linkage and association tests to an appropriate series of genome DNA markers. GRANT =P01HD354580002 Description(Adapted from the applicant's description): To further investigate the anomalous neural systems in autistic disorder as a phenotype for genetic analysis, the investigators will perform high- resolution three-dimensional magnetic resonance imaging (MRI) scans in two childhood AD populations as the basis for subsequent complete morphometric analysis for computation of volume of whole brain, individual substructures, hemispheric regions, and application of specialized method of cortical localization and parcellation.